Conditions For Optimal Efficiency Research Articles

Removal Characteristics of Ni-Ferrite Oxide Film Formed on the Stainless Steel Surface in Fiber Laser Decontamination

Every nuclear facility has a limited operating life, at the end of which they must be shut down and decommissioned. For decommissioning, the removal of radioactive contaminants and demolition should be considered. Before nuclear power plants are decommissioned, the primary system, which is the most heavily contaminated, is decontaminated first, followed by decontamination of the surfaces of containment containers and buildings. This study examined the removal characteristics of Ni-ferrite coated on the stainless steel (STS304) specimen surface using an eco-friendly laser that generates little secondary waste, and derived the optimal efficiency conditions for laser decontamination. In this study, simulated oxide film specimens were fabricated by coating the STS304 substrate using non-radioactive Ni-ferrite. The experimental equipment for laser decontamination was a Q-switched fiber laser with an average power of 100 W. The laser beam was irradiated on the surface of the specimen according to the beam overlap rate. In addition, the characteristics of the decontaminated area and removal of the coating layer were checked using digital 3D microscopy, scanning electron microscope (SEM), and X-ray diffraction (XRD). The results of laser decontamination experiment indicated the possibility of coating layer removal with fewer scans as the x- or y-axis directions beam overlap rate increased. However, the surface was discolored when excessive overlaps occurred. This study provided basic data for laser decontamination applicable to the removal of Ni-ferrite oxide films on STS304.

Efficiency improvement strategy of fuel cell system based on oxygen excess ratio and cathode pressure two-dimensional optimization

Improving the commercial fuel cell system efficiency is critical to reducing hydrogen consumption and improving the operational economy. This paper studies the power consumption pattern of the air supply subsystem, the most power-consuming auxiliary components, aiming to improve the system’s efficiency. A method was proposed to get the extremum of the system net power by optimizing the oxygen excess ratio and cathode pressure. Mathematical models describing the fuel cell stack and air supply subsystem power characteristics were developed based on the mechanism analysis and estimation of unknown parameters. Then, a system net power model for energy efficiency optimization was developed. The operating conditions for optimal efficiency at a specific current density can be obtained by numerical calculation. To verify the method’s effectiveness, a series of experiments were conducted, and the results show that the proposed method can maximize system net power output at various current density conditions. Compared with the conventional oxygen excess rate based one-dimensional optimization, the two-dimensional method can improve system efficiency by 2.06%, offering a good application prospect.

Design of a CH3NH3PbI3/CsPbI3-based bilayer solar cell using device simulation

With lead-based light harvesters, perovskite solar cells (PSCs) have an efficiency of approximately 25.5%, making them a viable photovoltaic technology. The selection of the absorber materials for PSC in this work are (i) Cesium lead iodide (CsPbI3) with a 1.73eV bandgap as the first absorber layer, this halide imparts higher stability to perovskite solar cells (ii) CH3NH3PbI3 (MAPbI3) with a bandgap of 1.55eV is selected as the second absorber layer as this material provides better efficiency to the perovskite solar cells. SCAPS-1D simulation software is used to perform an efficiency analysis of perovskite-perovskite CsPbI3/MAPbI3 bilayer solar cell. For efficiency optimization of the perovskite-perovskite bilayer solar cell, we have tried to calibrate seven parameters of the cell. These parameters are (i & ii) selection of the electron and hole transport material (iii, iv & v) variation in the: defect density of bulk material, doping concentration and the thickness of absorber layers, (vi) variation in work function of front electrode (vii) varying interface defect density. After optimization, the efficiency (η) of bilayer PSC is estimated to be 33.54%. The other PV parameters observed in optimal efficiency condition are open-circuit voltage (VOC) = 1.34V, short-circuit current density (JSC) = 27.45 mA/cm2 and fill factor (FF) = 90.49%. The CsPbI3/MAPbI3 bilayer perovskite solar cell efficiency is roughly double the efficiency of single junction CsPbI3 or MAPbI3 PSC. Our analysis observed that the variation in the doping and defect density of narrow bandgap material profoundly impacts the efficiency of perovskite-perovskite bilayer solar cells compared to the wide bandgap material.

Investigation into the Hydrodynamic Noise Characteristics of Electric Ducted Propeller

Ducted propeller is a kind of special propeller widely used in unmanned underwater vehicles, its flow characteristics and hydrodynamic noise are very important for marine environmental protection and equipment concealment. The hybrid techniques based on the acoustic analogy theory are adopted in the present study to calculate the unsteady flow field and sound field characteristics of a ducted propeller. The full scale flow filed and hydro-acoustic sources of the propulsion system are simulated by Detached-Eddy computational fluid dynamics (CFD) method. Hydrodynamic noise are calculated by FWH equation based on the CFD results. The frequency domain and directivity of sound pressure level at different sound field monitoring points are analyzed at four navigational speeds. The results show that the navigational speed that is in the inflow condition of the ducted propeller play important roles in the flow structure and underwater radiated noise. Under the fixed impeller rotational speed, the propulsion efficiency of ducted propeller increases first and then decreases with the raise of navigational speed. The maximum errors of thrust and power between simulation and experiment values are 0.5% and 0.1% respectively, which means that the adopted DES numerical simulation method has high credibility in calculating the acoustic source. At impeller rotational speed of 2000 r/min, the best state of flow field distribution is at the navigational speed of 1.54 m/s, which is corresponding to the highest propulsion efficiency condition. The propeller noise presents dipole characteristic in all working conditions, and at the obvious blade passing frequency, multiple characteristics are presented; most of the noise contribution is also concentrated below four times of the blade passing frequency. The total sound pressure level of the hydrodynamic noise is the smallest at the optimal efficiency condition (the navigational speed is 1.54 m/s). At high navigational speed, the low frequency characteristics below blade passing frequency increase and the amplitude becomes larger. This indicates that the component of turbulent noise becomes more important with the increase of navigational speed. The research focuses on analyzing the relationship between the energy loss of the ducted propeller wake field and the noise level, and it is found that the vortex at the tail makes a certain contribution to the noise. The research conclusions could provide some reference for the acoustic performance evaluation and noise reduction optimization of ducted propeller design as well as the improvement of UUV stealth performance.

Performance test of optimal denitration efficiency of a 350MW unit under the background of new power system

With the establishment of the goal of “carbon peaking and carbon neutralization”, a new power system based on new energy is proposed. With the rapid development of ultra-high voltage external power and new energy in Shandong power grid, the difficulty of system peak regulation is increasing. At present, the peak regulation is mainly based on direct regulating thermal power units. The capacity of pumped storage power stations is limited and there are no gas-fired generating units, which also leads to serious shortage of other flexible regulation resources that Shandong power grid can call. In 2022, Shandong Province plans to implement the renewable energy multiplication plan, and it is expected that the installed capacity of new energy will account for 38%. With the large-scale access of new energy, the “double high” characteristics of the power system are highlighted, and the technical characteristics and stability mechanism of the power grid will undergo profound changes. In the new power system with new energy as the main body, the role of thermal power generation has gradually changed from the electric power source to the regulating power source. Under the variable load conditions, find the optimal efficiency conditions and provide necessary data for the optimal denitration efficiency operation.

Optimization analysis of structure parameters of downhole vortex tool based on CFD and orthogonal studies

Liquid loading is one of the most serious problems in the gas wells with low pressure and production. It limits the production severely, due to the high cost of other deliquification technologies. The downhole vortex tool is an economic and efficient way to alleviate the liquid loading, but the optimal efficiency conditions still not clearly. In this paper, gas–liquid two-phase flow passing through a downhole vortex tool is studied by numerical simulation to optimize the structural parameters (Helix angle, helix height, helix width) and operating envelope (superficial gas velocity and superficial gas velocity) of the vortex tool. The Euler–Euler approach and Reynolds stress turbulence model are used to calculate the vortex field. The experimental results show that the pressure gradient downstream of vortex tool agrees well with the numerical results. An orthogonal design method was used to evaluate the performance of the vortex tool with different structural and operating parameters. The range analysis results show that the optimal combination is A2B2C3D5E5(α = 45°, H = 6 mm, h = 15 mm, vsg = 18 m/s, vsl = 0.1 m/s), with the impact sensitively intensity to evaluate index of each factor as follows: A > E > B > D > C. The effective operating envelope of vortex tool is when superficial gas velocity range from 9 m/s to 16 m/s. The pressure gradient downstream of optimal tool decreased by about 20.3% compared to the original tool at the maximum value point.

Efficiency Comparison of PolyDADMAC Coagulant with Ferric Chloride in the Treatment of Ahvaz Drinking Water

Background& Objective: PolyDADMAC is used in water and waste water treatment as a primary organic coagulant which can neutralize colloidal material with negative charge and reduces sludge volume compared with Mineral coagulants. The aim of this study was to evaluate and compare of PolyDADMAC with ferric chloride as a coagulant on the removal of turbidity, Coliform and Organic matter from Ahvaz drinking water. Materials and Methods: This study was carried out in a lab scale and using a jartest device in Ahwaz water treatment. In this research, the coagulation of raw water was studied using PolyDADMAC alone, and mixed coagulant of PolyDADMAC and ferric chloride at various dose and ferric chloride alone were compared. The study range was selected for turbidity (NTU3850, 80), pH (9-5) and different concentrations of coagulant material .Data analysis was performed using Excel, SPSS software and one way ANOVA (p<0.05). Results: The optimal efficiency conditions of PolyDADMAC in turbidity 3850 NTU, pH=8, Flash Mix =120rpm and resulted in an optimum dose of 0.5 mg/L which the highest turbidity removal percentage was to be 99.84 in optimal dose of 0.5ppm of coagulant. The optimum doses of ferric chloride with PolyDADMAC were obtained at 15mg/L and 0/4mg/L, respectively. Under higher doses of PolyDADMAC, flocs showed stabilized in solution .In addition, PolyDADMAC also produced larger floc with higher settling velocity that need less time to settle. Conclusion: The results from the comparison of the effect of coagulants mentioned in the high turbidity removal (NTU 3850) indicate the good performance of PolyDADMAC as coagulant to ferric chloride Also, the results showed that the removal efficiency was affected by the initial turbidity so that the higher the initial turbidity, nwould be the more efficient the turbidity removal.

Vortex Dynamics in the Wake of Three Generic Types of Freestream Turbines

An analysis of the vortex dynamics in the wake of three different freestream turbine concepts is conducted to gain a better understanding of the main processes affecting the energy recovery in their wakes. The turbine technologies considered are the axial-flow turbine (AFT), the crossflow turbine (CFT), also known as the H-Darrieus turbine, and the oscillating-foil turbine (OFT). The analysis is performed on single turbines facing a uniform oncoming flow and operating near their optimal efficiency conditions at a Reynolds number of 107. Three-dimensional (3D) delayed detached-eddy simulations (DDES) are carried out using a commercial finite volume Navier–Stokes solver. It is found that the wake dynamics of the AFT is significantly affected by the triggering of an instability, while that of the CFT and the OFT are mainly governed by the mean flow field stemming from the tip vortices' induction.

Conditions for optimal efficiency of PCBM-based terahertz modulators

We demonstrate the conditions for optimal modulation efficiency of active terahertz modulators based on phenyl-C61-butyric acid methyl ester (PCBM)-silicon hybrid structures. Highly efficient active control of the terahertz wave modulation was realized by controlling organic film thickness, annealing temperature, and laser excitation wavelength. Under the optimal conditions, the modulation efficiency reached nearly 100%. Charge distributions measured with a near-field scanning microwave microscanning technique corroborated the fact that the increase of photo-excited carriers due to the PCBM–silicon hybrid structure enables the enhancement of active modulation efficiency.

Comparison of the wake recovery of the axial-flow and cross-flow turbine concepts

A detailed wake analysis of two different turbine concepts is conducted to gain a fundamental understanding of the main energy recovery processes at play in each case. An axial-flow turbine and a cross-flow turbine are considered. Both operate near their respective optimal efficiency conditions in a uniform oncoming flow and at a Reynolds number of 107. Three-dimensional Delayed Detached-Eddy Simulations (DDES) are carried out and the time-averaged Unsteady Reynolds-averaged Navier–Stokes (URANS) equations are used as a post-processing tool in order to assess the importance of the various contributions affecting the wake recovery quantitatively. It is found that the dominant mechanism is fundamentally different between the two turbine technologies. Indeed, while the axial-flow turbine's wake is strongly influenced by an instability phenomenon leading to a significant turbulent transport, the cross-flow turbine's wake recovery is found to be much more related to the mean spanwise velocity field. As a result, unlike the axial-flow turbine's wake dynamics which is highly dependent on the turbulent characteristics of the oncoming flow, the cross-flow turbine's wake is expected to be less sensitive to these turbulent characteristics but highly dependent on the geometric characteristics of the turbine such as the turbine's aspect ratio.

Reprint of : Quantum interference in a Cooper pair splitter: The three sites model

New generation of Cooper pair splitters defined on hybrid nanostructures are devices with high tunable coupling parameters. Transport measurements through these devices revealed clear signatures of interference effects and motivated us to introduce a new model, called the 3-sites model. These devices provide an ideal playground to tune the Cooper pair splitting (CPS) efficiency on demand, and displays a rich variety of physical phenomena. In the present work we analyze theoretically the conductance of the 3-sites model in the linear and non-linear regimes and characterize the most representative features that arise by the interplay of the different model parameters. In the linear regime we find that the local processes typically exhibit Fano-shape resonances, while the CPS contribution exhibits Lorentzian-shapes. Remarkably, we find that under certain conditions, the transport is blocked by the presence of a dark state. In the non-linear regime we established a hierarchy of the model parameters to obtain the conditions for optimal efficiency.

Rapid design approach of optimal efficiency magnetic resonant wireless power transfer system

A rapid design approach to achieve the optimal efficiency in a magnetic resonant wireless power transfer (MR-WPT) system is presented. A concise design guideline is provided to determine the optimal efficiency condition and related coupling coefficients. Experimental validations are demonstrated by both simulation and measurement results of a 6.78 MHz MR-WPT system prototype with the maximum efficiency of 76.1% at a 50 mm distance between transmitter and receiver.

Quantum interference in a Cooper pair splitter: The three sites model

New generation of Cooper pair splitters defined on hybrid nanostructures are devices with high tunable coupling parameters. Transport measurements through these devices revealed clear signatures of interference effects and motivated us to introduce a new model, called the 3-sites model. These devices provide an ideal playground to tune the Cooper pair splitting (CPS) efficiency on demand, and displays a rich variety of physical phenomena. In the present work we analyze theoretically the conductance of the 3-sites model in the linear and non-linear regimes and characterize the most representative features that arise by the interplay of the different model parameters. In the linear regime we find that the local processes typically exhibit Fano-shape resonances, while the CPS contribution exhibits Lorentzian-shapes. Remarkably, we find that under certain conditions, the transport is blocked by the presence of a dark state. In the non-linear regime we established a hierarchy of the model parameters to obtain the conditions for optimal efficiency.

Estimation of population mean in post-stratified sampling using known value of some population parameter(s)

Following Khoshnevisan et.al. (2007) and Koyuncu and Kadilar (2009), this paper develops a general family of combined estimators of the population mean in post-stratified sampling (PSS) scheme, using known values of some population parameters of an auxiliary variable. Properties of the proposed family of estimators, including conditions for optimal efficiency, are obtained up to first order approximations. The results are illustrated empirically.

Towards a global control strategy for induction motor: Speed regulation, flux optimization and power factor correction

A great deal of interest has been paid to induction machine control over the last years. However, most previous works have focused on the speed/flux/torque regulation supposing the machine magnetic circuit to be linear and ignoring the machine power conversion equipments. The point is that speed regulation cannot be ensured in optimal efficiency conditions, for a wide range of speed-set-point and load torque, unless the magnetic circuit nonlinearity is explicitly accounted for in the motor model. On the other hand, the negligence of the power conversion equipments makes it impossible to deal properly with the harmonic pollution issue due to ‘motor – power supply grid’ interaction. This paper presents a theoretical framework for a global control strategy of the induction machine and related power equipments. The proposed strategy involves a multi-loop nonlinear adaptive controller designed to meet the three main control objectives, i.e. tight speed regulation for a wide range speed-reference variation, flux optimization for energy consumption and power factor correction (PFC). Tools from the averaging theory are resorted to formally describe the control performances.

Simulation of Steady-State Methanol Flux through a Model Carbon Nanotube Catalyst Support

Nonequilibrium molecular dynamic (MD) simulations were performed to show transport of a water–methanol solution through a novel catalysis membrane, constructed from single-walled carbon nanotubes (CNTs) with a Pt monolayer catalyst at the membrane’s exit. These calculations are directed toward understanding methanol transport dynamics in the CNT core, past the Pt coating, and to find the conditions for optimal efficiency as a function of both CNT diameter and pressure. Probability density function calculations for various methanol observables show that methanol primarily travels along the pore wall, which is ideal for methanol to interact efficiently with a catalyst at the exit. From the percent of methanol that passed through the pores within the minimum of the Lennard-Jones potential (21/6σPt–O), we estimate the residence time of methanol flux past the Pt monolayer in the range of 2–6 ps. The mass transport percent efficiency of the methanol flowing past the catalyst site is as high as 86% for (10,10) C...

Conditions for Optimal Efficiency of Relative MDS

In this paper, the relative multidimensional scaling method is investigated. This method is designated to visualize large multidimensional data. The method encompasses application of multidimensional scaling (MDS) to the so-called basic vector set and further mapping of the remaining vectors from the analyzed data set. In the original algorithm of relative MDS, the visualization process is divided into three steps: the set of basis vectors is constructed using the k-means clustering method; this set is projected onto the plane using the MDS algorithm; the set of remaining data is visualized using the relative mapping algorithm. We propose a modification, which differs from the original algorithm in the strategy of selecting the basis vectors. The experimental investigation has shown that the modification exceeds the original algorithm in the visualization quality and computational expenses. The conditions, where the relative MDS efficiency exceeds that of standard MDS, are estimated.

Thrust production and wake structure of a batoid-inspired oscillating fin

Experiments are reported on the hydrodynamic performance of a flexible fin. The fin replicates some features of the pectoral fin of a batoid fish (such as a ray or skate) in that it is actuated in a travelling wave motion, with the amplitude of the motion increasing linearly along the span from root to tip. Thrust is found to increase with non-dimensional frequency, and an optimal oscillatory gait is identified. Power consumption measurements lead to the computation of propulsive efficiency, and an optimal efficiency condition is evaluated. Wake visualizations are presented, and a vortex model of the wake near zero net thrust is suggested. Strouhal number effects on the wake topology are also illustrated.

Voltammetric study of Sn(II) reduction on a glassy-carbon electrode from sulfate-tartrate baths

The reduction of Sn(II) from sulfate-tartrate baths on a glassy-carbon electrode is studied. The influence of the tartrate anion and Sn(II) concentrations and the solution pH on the shape of the voltamograms and on the efficiency of the electrodeposition process is examined. A reaction scheme to explain the results is proposed. The voltammetric and anodic stripping analysis of the electrodeposition process shows that the optimal efficiency conditions to obtain Sn deposits are bath solutions without excess of tartrate ligand, not excessively high pH, and low overpotentials.

Energy efficiency optimisation in synchronous reluctance motor drives

A method for energy efficiency optimisation of synchronous reluctance motor drives is presented. The proposed method is implemented both in current vector and voltage source V/f controlled schemes. Based on theoretical considerations, two optimal efficiency conditions that determine the optimal air-gap flux and the optimal d-axis current for the two control schemes are derived. The proposed controllers do not affect the cost and the complexity of the drive. Moreover, they are easily implemented, since an experimental procedure is used to determine their parameters, and therefore knowledge of the loss model is not required. Experimental results are presented to validate the proposed control methods and the resulting improvements.